Biochemistry of Hair Cycling

The terminal human hair at the scalp is transformation of a vellus hair to terminal hair which undergoes a cyclical pattern of hair growth (anagen), regression (catagen) and relative quiescence (telogen). A hair is proteincious fibre with extreme tensile strength. The hair is dead outside scalp and therefore can be cut from outside. The hair grows under dermis from its hair follicle which is bulbous mass of cells with is blood supply and erector muscles.

The most unique feature of hair biology is hair growth and its cycling pattern. But why and how does hair follicle cycle is largely unclear. The signals for hair growth (the anagen stage) are in the process of being characterised. Androgens are the main regulator of changes in human hair. In genetically predisposed individuals, androgens transform terminal scalp hair into thin miniaturised hair called vellus hair, causing baldness. This pattern is baldness known as androgenic alopecia is more prevalent in males. In females, there is general and dispersed thinning of hair.

The genetics of hair recycling largely remain unclear but a number of factors play a significant role in male pattern hair thinning. In india, most people tend to wash hair with soap leading to poor scalp condition and the pH of the skin becomes highly alkaline.

• Do not wash hair with a soap; wash only with a mild shampoo.


• Do not use a harsh shampoo which make hair rough and lustreless


• Do not shampoo hair daily with a shampoo. Use a pH balanced shampoo upto twice a week.


• Exercise daily.

The hair during its cycle is subject to disease :




Alopecia

Abnormal hair loss




Androgenic alopecia

Miniaturisation of genetically pre-disposed hair follicles at the top of scalp and conversion of terminal hair into vellus thin hair




Alopecia aerate

Patchy hair loss possibly due to autoimmune defects




Cicatrical alopecia

Destruction of hair follicles due inflammation and other causes.




Anagen effluvium

Sudden shedding of hair caused by interruption of hair growth anagen phase, (like due to chemotherapy of cancer patient)




Telogen effluvium

Poorly defined thinning of scalp hair, usually due to physical trauma of emotional stress